Pulping machine



June 23, 1964 E LEJEUNE ETAL 3,138,336

PULPING MACHINE Filed July l0, 1961 3 Sheets-Sheet vl June 23, 1964 E. LEJEUNE ETAL 3,138,336

PULPING MACHINE Filed July l0, 1961 5 Sheets-Sheet 2 June 23 1964 E, Ll-:JEUNE ETAL 3,138,335

PULPING MACHINE Filed July lo, 1961 s sheets-sheet 3 United States Patent O 3,138,336 PULFING MACHINE Emile Lejeune and Juliette Boutin, both of 44 Rue La Bootie, Paris, France Fied .fuiy 1Q, i961, Ser. No. 122,336 Claims priority, application France duly I3, 1960 Cairns. (Cl. 2411-73) This invention relates to pulping machines for the production of pulp from fibrous, e.g. Cellulosic, materials, such as are used in the paper industry.

The functions of such a machine can be regarded as twofold. It must act to break up or shred the raw fibrous stock, and it must screen the shredded stock to provide a pulp product of a prescribed degree of lineness. The rejects or tails of the screening operation are usually recycled through the machine for further shredding therein. The screening operation is of especial importance where the raw fibrous stock is apt to contain such hard foreign materials as various metallic or other hard objects which may be found Where the input stock comprises refuse paper and textiles and the like, but is necessary in other cases also.

In many conventional types of pulping machines, both the shredding and the screening processes are carried out simultaneously. For example, one Widely used type of pulping machine includes a cylindrical rotor revolving in a cylindrical stator, the rotor surface being formed with flutes or splines, and the stator surface being also formed with flutes or splines except over part of its circumferential extent in which said stator surface is formed as a screen. In such Ia machine the shredding and screening operations are performed over respective parts of each revolution of the rotor, i.e. both operations progress practically simultaneously. The discharge of screening rejects or tails cannot be performed efiiciently, and it is found that the resulting pulp product is of poor quality. The rejects build up in the side portions of the machine land must be cleared at frequent intervals.

Another type of pulping machine that has sometimes been used comprises a stator and a rotor which are of frustoconical form throughout their axial extent. Over a first axial length the stator surface is formed as a screen and the cooperating rotor surface is formed with splines or flutes or the like to force the stock through the screen, while over a further axial extent beyond the screen, both the stator and rotor are formed with cooperating splines or flutes to provide shredding means. This latter section of the machine is followed by a discharge chamber from which the materials are recycled through the machine. The relative proportion of recycled material in such a machine is extremely high so that the pulping efficiency is very low and the product is of poor grade.

It is noted that in the type of pulping machine last described, the machine can be regarded as including a first screening zone, followed by a shredding zone, followed by a discharge Zone. While, unlike the first class of machine discussed above, the shredding and screening functions are effectively separated in such a machine, the sequence in which these functions proceed is illogical, since the screening proceeds the shredding, whereby the recycle ratio is greatly increased, and the poor results obtained are ascribable for a major part to this illogical design.

It is, in contrast, an object of this invention to provide a pulping machine wherein the functions of shredding the raw stock and screening .the shredded stock (and subsidiarily, discharging the rejects or tailing of the screening operation) are performed separately and in the order stated. With such an arrangement experience has shown that the pulping process as a whole proceeds more uniformly and efficiently, the proportion of rejects that have to be recycled is greatly reduced, the feed is more uniform and can be made to proceed in a desirable helicoidal path, the rotor can be driven at greatly increased peripheral velocities, so that the overall efficiency of the pulping process is improved, and the quality of the pulp product enhanced. Objects of this invention are to accomplish the various desirable features just enumerated.

According to an aspect of the invention there is provided a pulping machine for shredding raw fibrous stock and screening the shredded stock to provide pulp, which comprises a first, diverging, frustoconical annular zone defined between relatively rotating surfaces including means for shredding the stock, a second, cylindrical annular Zone continuous with the first zone and defined between relatively rotating surfaces including means for screening the shredded stock, a third zone connected with the end ofthe second zone remote from the first zone for collecting and discharging screening tails, and inlet means connecting, preferably tangentially, with the narrower end of the first zone for feeding fibrous stock thereinto for continuous circulation through the zones.

An exemplary embodiment of the invention will now be described for purposes of illustration but not of limitation with reference to the accompanying drawings, wherein:

FIG. 1 is a longitudinal view of the improved pulping machine the upper half of the figure being an axial section and the lower half being an outer elevation of the rotor with the stator removed;

FIG. 2 is a cross section on the line II-II of FIG. 1';

FIG. 3 is a cross section on the line III-III of FIG. l;

FIG. 4 is an axial sectional view of a portion of the stator of the pulping machine.

The pulping apparatus shown comprises `an outer stator structure which includes a frusto-conical diverging stator section 2 followed by a cylindrical stator section 2'; and an inner rotor structure which correspondingly includes the frusto-conical rotor section 1 and cylindrical rotor section 1. The rotor 1-1' is secured on a shaft suitably journalled in bearings in the respective ends of the stator 2-2, as schematically shown.

According to the invention and as will presently appear the frustoconical section 1-2 of the stator-rotor assembly defines the shredder zone of the pulping machine and is generally designated in FIG. 1 as zone I, while the cylindrical section 1-2 defines the screening zone generally designated II. Advantageously zones I and II are of approximately equal length.

Cellulosic stock is fed tangentially into the space between the stator and rotor structures through a tangential feed pipe 3 connecting with the shredding zone adjacent the narrower end of it, and such material will be fed through said space as indicated by arrows F in FIG. l along a generally helical path when the rotor is rotated from a suitable power source. In the shredding zone I, both the rotor section 1 and stator section 2 are formed in their spaced, facing surfaces with generally longitudinal splines as will appear at 4 and 5 respectively in FIG. 2.

The taper of sections 1 and 2 may be of the order of 10%.

Preferably, as shown on FIG. 4, the stator splines 5, while being of substantially uniform depth along their axial extent, are inclined or skewed by a small angle, say 2 or 3 to the generatrices of the frustoconical stator surface in the same direction as that of rotation of the rotor. Further, the radially outer edges of the stator splines or flutes are preferably rounded (see FIG. 2). It has been found that the skewing of the stator utes substantially reduces the power consumed for a given shredding operation, and that said skewing feature coupled with the rounding-off of the outer spline surfaces facilitates the shredding process.

In the screening zone II, the rotor section 1' is formed with liutes or splines 4' similar to and forming extensions of the fiutes 4, but having a gradually decreasing depth from the inlet to the outlet end of the section, so as to take into account the reduction in rate of flow of pulp towards the tails end of the screen and maintain a maximum amount of pulp at the heads end. In the screening zone II, the wall of the stator section 2 is formed as a screen 6 of suitable mesh size, extending over the full side area of stator section 2'. l

The stator section 2 is formed at its lower end with a collector chamber 11 which collects all of the pulp material forced outwards through the stator screen, and connecting with a pulp outlet 12.

The wall of rotor section 4 terminates short of the corresponding end wall of the stator 2' at the outlet end of the unit, so as to provide an end chamber 8 which constitutes the tails discharge zone, or zone III, of the apparatus. Thus the residual shredded stock that does not pass through the stator screen 6 collects in this end chamber or zone whence it is discharged through tailing outlet 9 to be preferably combined with fresh cellulosic stock entering at 3 so as to recycle through the apparatus. Means are shown at 10 for delivering water through the end chamber 8 to facilitate the discharge of the tails, and valves are correspondingly shown in the water inlet pipe 10 and tails discharge pipe 9. The delivery of water is, of course, optional.

According to a further preferred feature of the invention, the end part of rotor section 1 adjacent the discharge chamber 8 is preferably formed with radial vanes 13 to facilitate the discharge of the tails from the discharge chamber 8.

Desirably, the average diameter of the stator and rotor in the screening zone is not less than about 500 mm. The rotor is rotated at a suitable angular rate so as to provide a linear peripheral velocity preferably higher than 30 meters per second, e.g. 50 to 60 meters per second or more.

In operation, cellulosic stock fed into the apparatus through inlet 3 is successively shredded, screened and discharged in the respectives zones I, II and III defined above, and it will be appreciated readily that in each of these zones the material is exposed to optimum processing conditions in respect to the particular requirements of the operations being carried out in the zone; a situation not heretofore obtaining in pulping machinery of any of the conventional types known to the applicants.

rI `hus, in regard to the shredding zone, a uniform helical feed of the stock through this zone cannot be achieved otherwise than by using the frustoconical configuration shown, together with a tangential feed inlet as at 3. Prior pulping units of the wholly cylindrical type could not obtain such a desirable helical advance of the shredded materials, even by the application of pressure feed. Other types of pulpers were wholly conical throughout; but in such case, while the advance of the materials through the shredding zone is satisfactory, the screening operation is poor, since experience shows that a conical screen has a considerably lower efficiency than a cyclindrical one for a given peripheral rotor velocity.

Further, with the arrangement described, it is found that there is no propensity to lateral rejection of the stock at the inlet of the screening zone, so that it is unnecessary to dilute the pulp for eliminating such rejects which would otherwise tend to build up into a compact mass preventing operation of the apparatus.

A clearcut separation between the shredding and screening operations is had. The shredding process can be conducted at high speed under best possible conditions, since the conical shredder elements are designed for maximum effectiveness throughout their axial extent and periphery; thus the shredding process can be effectively pushed to a more advanced degree of completion before the screening is commenced.

Because the screening surface is cylindrical, the screening process can be conducted at higher speed with excellent efficiency, and provides an improved grade of pulp product.

The necessary recycling ratio is held to a minimum.

It is found that in the operation of a pulper according to the invention, owing to the continuous helical feed of material through the conical shredding zone and thence through the screening and discharge zones, a state of dynamic equilibrium is created in steady-state operation between the stock being shredded, the stock being screened and the rejects being discharged, and that by a suitable adjustment of the discharge valve 14 to provide an appropriate discharge and throughtiow rate for the material in the apparatus, and improved yield is obtained and power consumption is reduced, while the over-all quality of the pulp product is improved.

Thus with 3% cellulosic pulp stock, the operation of the improved pulping apparatus described has been compared with that of the more conventional cylindrical and all-conical types mentioned above, with the following results:

With apparatus having a screening surface area of 20 decimeters square, the fully-cylindrical unit required a power input of from 8 to 10 horsepower per 100 lig/hr. production rate, i.e. an efficiency factor of about 2,500 kg./hr. of pulp of average grade.

The all-conical apparatus, of the type wherein screening proceeds shredding, gives a production rate of only 600 lig/hr. of a pulp product of somewhat higher grade, but at the expense of a prohibitive power input which rises to 20 H.P. per 100 kg./hr. production.

With the improved pulper described, other factors remaining equal, a production of 3000 kg./hr. of excellent quality pulp is obtained with a power input of only 6 to 8 horsepower per 100 kg.

What we claim is:

1. A pulping machine having diverging frustoconical relatively rotatable wholly impervious surfaces defining a first annular zone therebetween and cooperating projections on said surfaces for shredding fibrous stock in said first zone; cylindrical relatively rotatable surfaces defining a second annular zone therebetween contiguous with the larger end of said first zone, the outer one of said cylindrical surfaces being in the form of a screen and the other of said cylindrical surfaces having projections thereon for forcing shredded stock through said screen; an outlet for screened pulp connecting with a side of the second zone through said screen defining the outer cylindrical surface thereof; a discharge chamber connecting with the end of the second annular zone remote from the first zone and defining a third zone for the discharge of screening tails from said machine; and inlet means connecting tangentially with the narrower end of the first annular zone to feed stock thereto for continuous helical advance of said stock through the first zone to be shredded therein and thence for advance through said second zone to be screened therein.

2. A pulping machine having a shredding section cornprising spaced, cooperating, generally frustoconical wholly impervious stator and rotor surfaces and cooperating means on said surfaces for shredding pulp stock therebetween; and a screening section comprising spaced cooperating, generally cylindrical stator and rotor surfaces, said cylindrical stator surface being formed as a screen for screening the shredded stock therethrough; said screening section being arranged contiguous to, and in axial alignment with said shredding section for continuous feed of the pulp through the shredding section and thence to and through the screening section; tangential inlet means for feeding pulp into the space between said surfaces of the shredding section adjacent the end of the latter remote from said screening section; outlet means connected for receiving screened pulp passing through said screen of said screening section; and a discharge section disposed axially beyond the screening section and deiining a space communicating with the space between said surfaces of the screening section at the end of the latter remote from said shredding section for collecting screening rejects from said screening section.

3. A pulping machine having a stator comprising a Wholly impervious diverging frustoconical section and a cylindrical section contiguous therewith, and a rotor comprising a frustoconical section and a contiguous cylindrical section respectively cooperating with said frustoconical and cylindrical stator sections to define annular spaces therebetween; both said frustoconical sections having cooperating shredding means on the facing surfaces thereof; and said cylindrical section of the stator being formed as a screen; tangential inlet means for feeding pulp into the narrower end of the annular space deiined between said frustoconical sections; outlet means connected for collecting screened pulp material passing through said screen; and discharge means connected with the discharge end of the space between said cylindrical sections for discharging reject material therefrom.

4. A pulping machine comprising an outer stator having a diverging frustoconical section and a cylindrical section contiguous therewith; an inner rotor having a frustoconical section and a cylindrical section respectively cooperating with said frustoconical and cylindrical stator sections to define annular spaces therebetween; an inlet connecting tangentially with the narrower end of said frustoconical stator section for feeding fibrous stock into the machine; cooperating iiuted means on the facing surfaces of said frustoconical sections extending generally longitudinally thereof for shredding said brous stock; the cylindrical stator section being formed as a screen; uted means on the outer surface of said cylindrical rotor section substantially contiguous with said iirstmentioned iiuted means on the frustoconical rotor section for forcing the shredded stock through said screen;

outlet means connected with the cylindrical stator section at the outside of said screen to collect screened pulp material forced through the screen; and discharge means connected with the end of the cylindrical stator section axially beyond said screen for discharging reject stock that has failed to pass the screen.

5. The pulping machine as in claim 4, wherein said frustoconical sections have a taper of about 10% with respect to the axis thereof.

6. The pulping machine as in claim 4, wherein at least some of said iiuted means are skewed with respect to the generatrices of said surfaces.

7. The pulping machine claimed in claim 4, wherein the iluted means of the cylindrical rotor section are of gradually decreasing depth in the direction of the feed of the stock.

8. The pulping machine as in claim 4, wherein said fluted means of the stator consist of alternating elongated projections and grooves having rounded cross-sectional configurations.

9. The pulping machine as in claim 4, wherein said discharge means includes a discharge chamber, axially beyond said cylindrical section of the stator and having a discharge outlet and an inlet connected therewith for delivering water through the discharge chamber for the dicharge of the reject stock through the discharge outlet.

10. The pulping machine as in claim 9, wherein the end of said rotor adjacent said discharge chamber has vane means thereon for displacing the reject stock in said discharge chamber.

References Cited in the file of this patent UNITED STATES PATENTS 647,129 Beall Apr. 10, 1900 812,122 Fassett Feb. 6, 1906 2,524,884 Clerk Oct. 10, 1950 2,980,350 Lejeune Apr. 18, 1961 

1. A PULPING MACHINE HAVING DIVERGING FRUSTOCONICAL RELATIVELY ROTATABLE WHOLLY IMPERVIOUS SURFACES DEFINING A FIRST ANNULAR ZONE THEREBETWEEN AND COOPERATING PROJECTIONS ON SAID SURFACES FOR SHREDDING FIBROUS STOCK IN SAID FIRST ZONE; CYLINDRICAL RELATIVELY ROTATABLE SURFACES DEFINING A SECOND ANNULAR ZONE THEREBETWEEN CONTIGUOUS WITH THE LARGER END OF SAID FIRST ZONE, THE OUTER ONE OF SAID CYLINDRICAL SURFACES BEING IN THE FORM OF A SCREEN AND THE OTHER OF SAID CYLINDRICAL SURFACES HAVING PROJECTIONS THEREON FOR FORCING SHREDDED STOCK THROUGH SAID SCREEN; AN OUTLET FOR SCREENED PULP CONNECTING WITH A SIDE OF THE SECOND ZONE THROUGH SAID SCREEN DEFINING THE OUTER CYLINDRICAL SURFACE THEREOF; A DISCHARGE CHAMBER CONNECTING WITH THE END OF THE SECOND ANNULAR ZONE REMOTE FROM THE FIRST ZONE AND DEFINING A THIRD ZONE FOR THE DISCHARGE OF SCREENING TAILS FROM SAID MACHINE; AND INLET MEANS CONNECTING TANGENTIALLY WITH THE NARROWER END OF THE FIRST ANNULAR ZONE TO FEED STOCK THERETO FOR CONTINUOUS HELICAL ADVANCE OF SAID STOCK THROUGH THE FIRST ZONE TO BE SHREDDED THEREIN AND THENCE FOR ADVANCE THROUGH SAID SECOND ZONE TO BE SCREENED THEREIN. 